U.S. patent number 7,470,114 [Application Number 11/460,494] was granted by the patent office on 2008-12-30 for rotor blade for a wind energy turbine.
This patent grant is currently assigned to General Electric Company. Invention is credited to Laurent Bonnet.
United States Patent |
7,470,114 |
Bonnet |
December 30, 2008 |
Rotor blade for a wind energy turbine
Abstract
The rotor blade for a wind energy turbine comprising a
longitudinal shell defining a root to be connected to a hub of a
rotor, a tip, a forward edge and a rearward edge, the shell having
a spar including two spar caps connected via at least one shear web
arranged between the forward and rearward edges of the shell and
extending in the longitudinal direction of the shell, and a
structural damping system arranged within the shell and having a
pendulum including a dumped sandwich beam and a mass element
located at one end of the beam. The beam comprises a sandwich
structure including at least three layers comprising at least one
damping middle layer arranged between and connected to outer layers
of an elastic material. The sandwich beam is connected to the at
least one shear web in a cantilevered manner such that the mass
element is proximal to the tip of the shell and the beam can be
oscillated in a direction towards and away from the forward and
rearward edges of the shell.
Inventors: |
Bonnet; Laurent (Mesum,
DE) |
Assignee: |
General Electric Company
(Schenectady, NY)
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Family
ID: |
35519770 |
Appl.
No.: |
11/460,494 |
Filed: |
July 27, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070041829 A1 |
Feb 22, 2007 |
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Foreign Application Priority Data
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Aug 17, 2005 [EP] |
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05107564 |
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Current U.S.
Class: |
416/226;
416/500 |
Current CPC
Class: |
F03D
80/00 (20160501); F03D 1/06 (20130101); F16F
7/104 (20130101); Y02E 10/722 (20130101); Y02E
10/721 (20130101); Y10S 416/50 (20130101); Y02E
10/72 (20130101); F05B 2240/30 (20130101); F05B
2260/96 (20130101) |
Current International
Class: |
F04D
29/66 (20060101) |
Field of
Search: |
;416/80,226,500,103,106,107,233 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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19741627 |
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Mar 1999 |
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DE |
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WO 95/21327 |
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Aug 1995 |
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WO |
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WO 96/11337 |
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Apr 1996 |
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WO |
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Primary Examiner: Edgar; Richard
Attorney, Agent or Firm: GE Global Patent Operation
Claims
The invention claimed is:
1. A rotor blade for a wind energy turbine, comprising a
longitudinal shell defining a root that connects to a hub of a
rotor, a tip, a forward edge and a rearward edge, the shell having
a spar including at least one shear web arranged between the
forward and rearward edges of the shell and extending in the
longitudinal direction of the shell, a vibration damper arranged
within the shell and having a pendulum including a beam and a mass
element located at one end of the beam, the beam comprising a
sandwich structure including at least three layers comprising at
least one damping middle layer arranged between and connected to
outer layers of an elastic material, and the beam is connected to
the at least one shear web in a cantilevered manner such that the
mass element is proximal to the tip of the shell and the beam can
be oscillated between the forward and rearward edges of the
shell.
2. The rotor blade according to claim 1, wherein the at least one
middle layer of the sandwiched cantilever beam comprises a
viscoelastic, elastomeric or frictional material.
3. The rotor blade according to claim 1, further comprising bump
stoppers arranged within the shell for damping a potential contact
of the mass element of the pendulum with the shell.
4. The rotor blade according to claim 1, wherein the outer layers
of the sandwiched cantilever beam comprise metal.
5. The rotor blade according to claim 4, wherein the metal is
steel.
6. The rotor blade according to claim 1, wherein the sandwiched
cantilever beam is fastened to the at least one shear web of the
spar of the shell.
7. The rotor blade according to claim 6, wherein the sandwiched
cantilever beam is fastened to the at least one shear web by means
of fastening bolts extending through the at least one shear web of
the spar of the shell and through the beam.
8. The rotor blade according to claim 6, wherein the sandwiched
cantilever beam is laminated and glued to the at least one shear
web by means of integrated lamination and fixtures extending
through the at least one shear web of the spar of the shell and
through the beam.
Description
BACKGROUND
1. Field of The Invention
The present invention relates to a passive structural damping
system for a wind turbine blade and, in particular, to a rotor
blade for a wind energy turbine comprising a damping system for
damping at least the first edge-wise structural bending mode of the
wind turbine blade.
2. Related Prior Art
The blades of the rotor of a wind energy turbine are subjected to
diverse edge-wise structural bending modes, meaning that the rotor
blades are oscillating within the plane of rotation. Among these
bending modes the first edge-wise structural bending mode typically
has a merely poor structural damping effect (about 1% only)
resulting from a typical blade construction. The first edge-wise
structural bending mode typically has a frequency from 1-5 Hz and
can be easily excited by wind turbulences. The first edge-wise
structural bending mode can induce dynamic loads to all the
components of the drive shaft of the wind energy turbine such as
high blade root bolting dynamic loads at resonance frequency, high
dynamic torque variation, increasing gearbox gear stages and
bearings wear, and possibly high dynamic loads to the main bearing
and bedplate, generating additional fatigue.
It is basically known to provide structural damping of the first
edge-wise bending mode by means of a moving mass at the tip of the
blade. U.S. Pat. No. 6,626,642 suggests to provide an oscillating
mass on an articulated shaft connected to the shell of the blade by
means of a specific loss bearing. WO-A-95/21327 provides a
classical mass-spring-damper arranged within the tip portion of the
shell of a rotor blade.
The known damping systems are complicated in construction and
difficult to integrate into the internal construction of a rotor
blade. Accordingly, there is a need for a damping system which is
easy to manufacture and install, provides robustness and is
failure-free and, accordingly, substantially maintenance-free.
SUMMARY OF THE INVENTION
The problems listed above are solved according to the invention by
providing a rotor blade for a wind energy turbine comprising a
longitudinal shell defining a root that connects to a hub of a
rotor, a tip, a forward edge and a rearward edge, the shell having
a spar including at least one shear web arranged between the
forward and rearward edges of the shell and extending in the
longitudinal direction of the shell, a vibration damper arranged
within the shell and having a pendulum including a beam and a mass
element located at one end of the beam, the beam comprising a
sandwich structure including at least three layers comprising at
least one damping middle layer arranged between and connected to
outer layers of a elastic material, and the beam is connected to
the at least one shear web in a cantilevered manner such that the
mass element is proximal to the tip of the shell and the beam can
be oscillated between the forward and rearward edges of the
shell.
The present invention provides a wind energy turbine blade passive
structural damping system comprising a sandwiched beam connected to
the internal construction of the rotor blade in a cantilever manner
such that the beam is bent while oscillating towards and away from
the forward and rearward edges of the blade. The sandwiched
cantilever beam comprises at least three layers of different
materials, the outer (upper and lower) ones being elastic while the
middle layer comprises a damping material such as a viscoelastic,
elastomeric, or frictional material. The cantilever beam can
comprise several damping layers arranged between the elastic layers
while also additional elastic and damping layers can be arranged
outside of the layer arrangement mentioned before. In other words,
the sandwiched cantilever beam comprises several elastic and
damping layers laminated onto each other.
In particular, the laminated sandwiched cantilever beam comprises a
viscoelastic or elastomeric damping layer encompassed by upper and
lower steel layers or layers of another elastic metal. Instead of
an elastomeric or viscoelastic damping layer, the damping layer may
comprise friction generating materials such as entangled fibres or
mesh wires, e.g. made of metal or plastics or for enhancing
friction, by contact surface machining of the interface of two
material layers of the sandwiched cantilever beam contacting each
other. The damping effect of the elastic sandwiched cantilever beam
according to the invention results from the generation of shear
damping losses in the damping layer when the beam is bending.
Accordingly, each damping material which causes shear losses can be
used for the damping layer or damping layers of the cantilever
beam.
According to the invention, the sandwiched cantilever beam
functions as a pendulum including the beam and a mass element
located at one end of the beam. It is to be noted that the mass
element need not be a separate element located at the one end of
the beam. The end portion of the beam as such can be regarded as
the mass element although an additional mass element attached or
otherwisely integrated into or mounted to the end of the beam is
preferred in order to add additional mass to the beam. The
sandwiched cantilever beam oscillates within the plane of rotation
of the rotor blade. Due to its sandwich structure, the beam is
unlikely to oscillate or bend in a direction perpendicular to its
preferred bending direction. Accordingly, the sandwiched cantilever
beam according to the invention is sensitive to edge-wise
oscillations while preventing flap-wise oscillations which
generally stabilizes the rotor during operation.
In another aspect of the present invention the blade comprises
internal bump stoppers arranged for damping a potential contact of
the moving end of the sandwiched cantilever beam with the blade, in
order to limit sandwiched cantilever beam mass displacement within
the blade cavity
As mentioned before, the sandwiched cantilever beam is mechanically
connected to the internal stiffening construction of the blade.
This stiffening construction comprises a spar including spar caps
and at least one shear web connecting the spar caps. The sandwiched
cantilever beam can be directly fastened to the at least one shear
web preferably by fastening bolts and/or laminated and glued
extending through the at least one shear web and the sandwiched
cantilever beam. The at least one shear web can be encompassed, at
its end facing the sandwiched cantilever beam, by the outermost
layers of the sandwiched cantilever beam. However, it is also
possible that the sandwiched cantilever beam is connected at one
side of the at least one shear web only.
According to the invention there is provided a rotor blade with a
passive structural damping system formed as a pendulum made of a
cantilever beam fixed to a blade shear web. The pendulum provides
for a resonance of the cantilever beam occurring in the first
bending mode of the blade. The cantilever beam is provided as a
laminated sandwiched structure, in particular a laminated
steel/elastomer/steel sandwiched structure which irrespective of
the material used for the individual layers, can have many
superimposed layers. Damping occurs when the laminated sandwiched
cantilever beam is bending which creates shear damping losses in
the then shear constrained elastomer of damping material layer(s).
The major benefits of the damping system according to the invention
are damping addition can be up to 10 times of original blade
damping of at least first edge-wise blade structural mode with very
low added mass (typically less than 1%), mechanical construction
integration, easy of manufacture and installation, possibility to
upgrade existing blades, construction robustness, failure-safety by
principle and, substantially maintenance-free.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be explained in more detail referring to
the drawings in which
FIG. 1 shows an example of a three-blade wind energy turbine rotor
wherein a sandwiched cantilever beam is located in each of the
blades and connected to at least one of the respective shear webs
thereof,
FIG. 2 shows a cross-sectional view through one of the rotor blades
taken along the line II-II of FIG. 1,
FIG. 3 shows a horizontal cross-sectional view through the tip
portion of a rotor blade on a larger scale, and
FIG. 4 shows a cross-sectional view through the sandwiched
cantilever beam taken along the line IV-IV of FIG. 3.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 shows a front view of a rotor 10 for a wind energy turbine
comprising a hub 12 and three rotor blades 14 radially extending
from the hub 12. Each of the rotor blades 14 comprises a shell 16
defining a root 18 and a tip 20 limiting the longitudinal dimension
of the rotor blade 14 (see also FIG. 2). The shell 16 of each rotor
blade 14 further defines a leading or forward edge 22 and a
trailing or rearward edge 24 with respect to the direction of
rotation (see arrow 26 in FIG. 1) of the rotor 10. The construction
of the shell 16 of each rotor blade 14 further comprises a spar 28
which includes two spar caps 30,32 arranged within the shell 16,
and at least one shear web 34 extending within the shell 16 and
connecting the spar caps 30,32. The individual portions of the
shell 16 and its spar 28 comprise sandwiched and laminated
structures as basically known by those skilled in the art of
manufacturing rotor blades.
As can be seen from FIGS. 1 and 2 as well as from FIG. 3, at the
radially outward end of the at least one shear web 34 of each rotor
blade 14, there is attached a pendulum 36 functioning as a
counterweight for damping and neutralizing to a certain extent the
first edge-wise blade bending mode. This bending mode results in an
oscillation of each rotor blade 14 in the plane of rotation as
shown by the arrows 38 in FIG. 1.
According to the preferred embodiment of the present invention, the
pendulum 36 in each of the rotor blades 14 comprises a sandwiched
cantilever beam 40 with an additional mass element 42 attached to
one of the ends of the beam 40. The sandwiched cantilever beam 40
is fastened to the shear web 34 such that the mass element 42 is
proximal to the tip 20 of the blade 14. The cantilever beam 40 in
this embodiment comprises a laminated steel/elastomer/steel
sandwiched structure comprising a middle layer 44 of an elastomeric
or viscoelastic damping material and two outer layers 46 made of
steel. Those skilled in the art will recognize that other
combinations of damping and elastic materials for the individual
layers of the sandwiched cantilever beam layer can be used.
As can be further seen in FIG. 3, in this embodiment the outer
steel layers 46 at the end of the beam 40 attached to the shear web
34 project beyond the middle layer 44 so as to encompass the shear
web 34 at its opposite sides. Within this part of the beam 40 and
shear web 34 several fastening bolts 48 extend through the shear
web 34 and outer layers 46, thereby fastening the beam 40 and/or
laminated within the shear web 34 in an easy manner to the internal
stiffening construction of the blade 14.
In the extension of the oscillating movement path of the mass
element 42 of the pendulum 36 there are arranged bump stoppers 50
located at the inner sides of the shell 16 at its forward and
rearward edges 22,24, respectively. These bump stoppers 50 prevent
damage of the rotor blade 14 upon extreme oscillating movements of
the pendulum 36 which may occur when the rotor blades in the
operating orientation of the blade as shown e.g. in FIGS. 1 and 3,
are subjected to increased accelerations.
Although the invention has been described and illustrated with
reference to specific illustrative embodiments thereof, it is not
intended that the invention be limited to those illustrative
embodiments. Those skilled in the art will recognize that
variations and modifications can be made without departing from the
true scope of the invention as defined by the claims that follow.
It is therefore intended to include within the invention all such
variations and modifications as fall within the scope of the
appended claims and equivalents thereof.
* * * * *